1. Technical Field
Example embodiments of the present invention relate in general to the field of an access point scan method, and more particularly, to an access point scan method using an active scan scheme in a wireless LAN system.
2. Related Art
Various wireless communication technologies have been developed together with information communication technologies. Wireless local area network (WLAN) belonging to the wireless communication technologies is a technology allowing wireless internet access at home or business or at a designated service providing region by using a portable terminal, such as a personal digital assistant (PDA), a laptop computer, and a portable multimedia player (PMP) based on wireless frequency technologies.
As the standard of the WLAN, Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards have been developed. IEEE 802.11a provides a transmission speed of 54 Mbps by using an unlicensed band of 5 GHz. IEEE 802.11b provides a transmission speed of 11 Mbps by using direct sequence spread spectrum (DSSS) at 2.4 GHz. IEEE 802.11g provides a transmission speed of 54 Mbps by using orthogonal frequency division multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a transmission speed of 300 Mbps with respect to two spatial streams by using multiple input multiple output-OFDM (MIMO-OFDM). IEEE 802.11n supports a channel bandwidth of 40 MHz at the maximum, and provides a transmission speed of 600 Mbps.
As the propagation of the WLAN becomes more active and applications using the WLAN are diversified, there is an increasing need for a new WLAN technology capable of supporting a throughput higher than the data processing speed supported by IEEE 802.11n. WLAN technology for very high throughput (VHT) is one of the IEEE 802.11 WLAN technologies suggested to support a data processing speed of 1 Gps or more. As one of the VHT WLAN technologies, IEEE 802.11ac is developed as a standard for supporting a VHT at a frequency band of 5 GHz or below, and IEEE 802.11ad is developed as a standard for supporting a VHT at a frequency band of 60 GHz.
In a system based on the WLAN technology, an access point scan method includes an active scan method and a passive scan method. According to the active access point scan method, a station transmits a probe request frame, and an access point having received the probe request frame transmits a probe response frame in response to the received probe request frame.
Upon requesting responses from a plurality of undesignated access points by setting a service set identifier (SSID) of a probe request frame in a state of null, the station receives a probe response frame from the access points during a maximum probe response time Max_Probe_Response_Time, and requests access at an access point whose wireless environment is the most superior among the access points having transmitted probe response frames. That is, even after a probe response frame is received from an access point having a superior wireless environment, the station waits for the maximum probe response time to pass, and then requests an access at the access point, thereby causing waste of time.
In the position of an access point, the access point needs to respond in the form of a probe response frame at each of the probe request frames being received, so the response is unconditionally made without consideration of a wireless environment, thereby causing waste of wireless resources.